/*
 * Copyright (c) 1996-1999 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * Original code by Paul Vixie, available at glibc sources:
 * https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=resolv/inet_ntop.c
 *
 * "Saguified" by Silvio Clecio.
 */

#include <stdio.h>
#include <errno.h>
#include <string.h>
#ifdef _WIN32
#include <ws2tcpip.h>
#else
#include <unistd.h>
#include <sys/socket.h>
#endif
#include "inet.h"

#define NS_INT16SZ      2
#define NS_IN6ADDRSZ    16

#ifdef SPRINTF_CHAR
# define SPRINTF(x) strlen(sprintf/**/x)
#else
# define SPRINTF(x) (sprintf x)
#endif

/*
 * WARNING: Don't even consider trying to compile this on a system where
 * sizeof(int) < 4.  sizeof(int) > 4 is fine; all the world's not a VAX.
 */

static const char *inet_ntop4(const u_char *src, char *dst, socklen_t size);

static const char *inet_ntop6(const u_char *src, char *dst, socklen_t size);

/* char *
 * inet_ntop(af, src, dst, size)
 *	convert a network format address to presentation format.
 * return:
 *	pointer to presentation format address (`dst'), or NULL (see errno).
 * author:
 *	Paul Vixie, 1996.
 */
const char *
inet_ntop(int af, const void *src, char *dst, socklen_t size) {
    switch (af) {
        case AF_INET:
            return (inet_ntop4(src, dst, size));
        case AF_INET6:
            return (inet_ntop6(src, dst, size));
        default:
            errno = (EAFNOSUPPORT);
            return (NULL);
    }
    /* NOTREACHED */
}

/* const char *
 * inet_ntop4(src, dst, size)
 *	format an IPv4 address
 * return:
 *	`dst' (as a const)
 * notes:
 *	(1) uses no statics
 *	(2) takes a u_char* not an in_addr as input
 * author:
 *	Paul Vixie, 1996.
 */
static const char *
inet_ntop4(const u_char *src, char *dst, socklen_t size) {
    static const char fmt[] = "%u.%u.%u.%u";
    char tmp[sizeof "255.255.255.255"];

    if (SPRINTF((tmp, fmt, src[0], src[1], src[2], src[3])) >= size) {
        errno = (ENOSPC);
        return (NULL);
    }
    return strcpy(dst, tmp);
}

/* const char *
 * inet_ntop6(src, dst, size)
 *	convert IPv6 binary address into presentation (printable) format
 * author:
 *	Paul Vixie, 1996.
 */
static const char *
inet_ntop6(const u_char *src, char *dst, socklen_t size) {
    /*
     * Note that int32_t and int16_t need only be "at least" large enough
     * to contain a value of the specified size.  On some systems, like
     * Crays, there is no such thing as an integer variable with 16 bits.
     * Keep this in mind if you think this function should have been coded
     * to use pointer overlays.  All the world's not a VAX.
     */
    char tmp[sizeof "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255"], *tp;
    struct {
        int base, len;
    } best, cur;
    u_int words[NS_IN6ADDRSZ / NS_INT16SZ];
    int i;

    /*
     * Preprocess:
     *	Copy the input (bytewise) array into a wordwise array.
     *	Find the longest run of 0x00's in src[] for :: shorthanding.
     */
    memset(words, '\0', sizeof words);
    for (i = 0; i < NS_IN6ADDRSZ; i += 2)
        words[i / 2] = (src[i] << 8) | src[i + 1];
    best.base = -1;
    cur.base = -1;
    best.len = 0;
    cur.len = 0;
    for (i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++) {
        if (words[i] == 0) {
            if (cur.base == -1)
                cur.base = i, cur.len = 1;
            else
                cur.len++;
        } else {
            if (cur.base != -1) {
                if (best.base == -1 || cur.len > best.len)
                    best = cur;
                cur.base = -1;
            }
        }
    }
    if (cur.base != -1) {
        if (best.base == -1 || cur.len > best.len)
            best = cur;
    }
    if (best.base != -1 && best.len < 2)
        best.base = -1;

    /*
     * Format the result.
     */
    tp = tmp;
    for (i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++) {
        /* Are we inside the best run of 0x00's? */
        if (best.base != -1 && i >= best.base &&
            i < (best.base + best.len)) {
            if (i == best.base)
                *tp++ = ':';
            continue;
        }
        /* Are we following an initial run of 0x00s or any real hex? */
        if (i != 0)
            *tp++ = ':';
        /* Is this address an encapsulated IPv4? */
        if (i == 6 && best.base == 0 &&
            (best.len == 6 || (best.len == 5 && words[5] == 0xffff))) {
            if (!inet_ntop4(src + 12, tp, sizeof tmp - (tp - tmp)))
                return (NULL);
            tp += strlen(tp);
            break;
        }
        tp += SPRINTF((tp, "%x", words[i]));
    }
    /* Was it a trailing run of 0x00's? */
    if (best.base != -1 && (best.base + best.len) ==
                           (NS_IN6ADDRSZ / NS_INT16SZ))
        *tp++ = ':';
    *tp++ = '\0';

    /*
     * Check for overflow, copy, and we're done.
     */
    if ((socklen_t) (tp - tmp) > size) {
        errno = (ENOSPC);
        return (NULL);
    }
    return strcpy(dst, tmp);
}
